A mild P. jirovecii pulmonary infection is prevalent in more than half of the general adult population. Our results strengthen the concept that immunocompetent adults develop frequent self-limited reinfections throughout life and participate in the circulation of P. jirovecii as an infective reservoir for susceptible individuals.

Fresh-frozen lung and tracheal-aspirate specimens obtained from 112 infants who died in Santiago, Chile, during 1998-2000 were analyzed for the presence of Pneumocystis DNA, by use of nested DNA amplification of the large subunit mitochondrial rRNA, and for the presence of viruses, by use of culture and immunofluorescence. Pneumocystis DNA was detected in specimens from 45 (51.7%) of 87 infants who died in the community and from 5 (20%) of 25 infants who died in the hospital (P=.006). Primary infection with Pneumocystis was highly frequent among infants who die unexpectedly in the community. Infection with viruses was more common in infants who died in the hospital.

Fungal colonization with Pneumocystis is associated with increased airway mucus in infants during their primary Pneumocystis infection, and to severity of COPD in adults. The pathogenic mechanisms are under investigation. Interestingly, increased levels of hCLCA1 – a member of the calcium-sensitive chloride conductance family of proteins that drives mucus hypersecretion – have been associated with increased mucus production in patients diagnosed with COPD and in immunocompetent rodents with Pneumocystis infection. Pneumocystis is highly prevalent in infants; therefore, the contribution of Pneumocystis to hCLCA1 expression was examined in autopsied infant lungs. Respiratory viruses that may potentially increase mucus, were also examined. hCLCA1 expression was measured using actin-normalized Western-blot, and the burden of Pneumocystis organisms was quantified by qPCR in 55 autopsied lungs from apparently healthy infants who died in the community. Respiratory viruses were diagnosed using RT-PCR for RSV, metapneumovirus, influenza, and parainfluenza viruses; and by PCR for adenovirus. hCLCA1 levels in virus positive samples were comparable to those in virus-negative samples. An association between Pneumocystis and increased hCLCA1 expression was documented (P=0.028). Additionally, increasing Pneumocystis burden correlated with increasing hCLCA1 protein expression levels (P=0.017). Results strengthen the evidence of Pneumocystis-associated up-regulation of mucus-related airway responses in infant lungs. Further characterization of this immunocompetent host-Pneumocystis-interaction, including assessment of potential clinical significance, is warranted.

To understand the epidemiological significance of Pneumocystis detection in a lung tissue sample of non-immunosuppressed individuals, we examined sampling procedures, laboratory methodology, and patient characteristics of autopsy series reported in the literature. Number of tissue specimens, DNA-extraction procedures, age and underlying diagnosis highly influence yield and are critical to understand yield differences of Pneumocystis among reports of pulmonary colonization in immunocompetent individuals.

The primary infection by Pneumocystis of normal, healthy infants is asymptomatic and goes undiagnosed. Microscopy diagnosis of Pneumocystis was sought in lung impression smears (LIS) from two ~3-month-old infants dying unexpectedly in the community. Pneumocystis nuclei and cysts were identified using Hema-Gurr with subsequent Gomori–Grocott staining in the same spot documenting that these stains may be complementary. LIS provide for an observer–dependent, inexpensive, and ready-available method for detection of Pneumocystis in infant lungs.